The arched inferior border of the transverse muscle, F, Plate 30, expresses by its abrupt termination that some part is wanting to it; and this appearance, together with the fact that the fibres of this part of the muscle blend with those of the internal oblique and cremaster, and cannot be separated except by severing the connexion, at once suggests the idea that the cremaster is a derivation from both these muscles.
Assuming this to be the case, therefore, it follows that when the dissector removes the cremaster from the space L h, he himself causes this vacancy in the muscular parietes of the groin to occur, and at the same time gives unnatural definition to the lower border of the transverse and oblique muscles. In a dissection so conducted, the cord is made to assume the variable positions which anatomists report it to have in respect to the neighbouring muscles. But when we view nature as she is, and not as fashioned by the scalpel, we never fail to find an easy explanation of her form.
In the foetus, prior to the descent of the testicle, the cremaster muscle does not exist. (Cloquet, op cit.) From this we infer, that those parts of the muscles, E F, Plate 30, which at a subsequent period are converted into a cremaster, entirely occupy the space L h. In the adult body, where one of the testicles has been arrested in the inguinal canal, the muscles, E F, do not present a defined arched margin, above the vacant space L h, but are continued (as in the foetus) as low down as the external abdominal ring. In the adult, where the testicle has descended to the scrotum, the cremaster exists, and is serially continuous with the muscles, E F, covering the space L h; the meaning of which is, that the cremasteric parts of the muscles, E F, cover this space. The name cremaster therefore must not cancel the fact that the fibres so named are parts of the muscles, E F. Again, in the female devoid of a cremaster, the muscles, E F, present of their full quantities, having sustained no diminution of their bulk by the formation of a cremaster. But when an external inguinal hernia occurs in the female body, the bowel during its descent carries before it a cremasteric covering at the expense of the muscles E F, just in the same way as the testicle does in the foetus. (Cloquet.)
From the above-mentioned facts, viewed comparatively, it seems that the following inferences may be legitimately drawn:—1st, that the space L h does not naturally exist devoid of a muscular covering; for, in fact, the cremaster overlies this situation; 2nd, that the name cremaster is one given to the lower fibres of the internal oblique and transverse muscles which cover this space; and 3rd, that to separate the cremasteric elongation of these muscles, and then describe them as presenting a defined arched margin, an inch or two above Poupart’s ligament, is an act as arbitrary on the part of the dissector as if he were to subdivide these muscles still more, and, while regarding the subdivisions as different structures, to give them names of different signification. When once we consent to regard the cremaster as constituted of the fibres originally proper to the muscles, E F, we then are led to the discovery of the true relations of the cord in respect to these muscles.
On removing the transverse muscle, we expose the inguinal part of the transversalis fascia—the sixth inguinal layer, L h, Plate 30—K k, Plate 31. This fascia or membrane affords a general lining to the abdominal walls, in some parts of which it presents of a denser and stronger texture than in others. It is stretched over the abdomen between the muscles and the peritonaeum. The fascia iliaca, the fascia pelvica, and the fascia transversalis, are only regional divisions of the one general membrane. On viewing this fascia in its totality, I find it to exhibit many features in common with those other fibrous structures which envelope serous cavities. The transversalis fascia supports externally the peritonaeum, in the same way as the dura mater supports the arachnoid membrane, or as the pleural fascia supports the serous pleura. While the serous membranes form completely shut sacs, the fibrous membranes which lie external to those sacs are pierced by the vessels which course between them and the serous membranes, and afford sheaths or envelopes for these vessels in their passage from the interior to the external parts. The sheath, H h, Plates 30 and 31, which surrounds the spermatic vessels, and the sheath, R, Plate 31, which envelopes the crural vessels, are elongations of the fascia transversalis.
In the groin, the transversalis fascia, K k, Plate 31, presents, in general, so dense a texture as to offer considerable resistance to visceral pressure. Here it is stretched between the transverse muscle, F, Plate 31, and the peritonaeum, I. It adheres to the external surface of the peritonaeum, and to the internal surface of the transverse muscle, by means of an intervening cellular tissue. It is connected below to Poupart’s ligament, along the line of which it joins the fascia iliaca. It lines the lower posterior aspect of the rectus muscle, where this is devoid of its sheath; and it is incorporated with f, the conjoined tendon, thereby fencing the external abdominal ring. Immediately above the middle of Poupart’s ligament, this membrane, at the point marked h, Plate 30, is pouched into a canal-shaped elongation, which invests the spermatic vessels as far as the testicle in the scrotum; and to this elongation is given the names “fascia spermatica interna” (Cooper), “fascia infundibuliform” (Cloquet). The same part, when it encloses an external oblique hernia, is named “fascia propria.” The neck or inlet of this funnel-shaped canal is oval, and named the “internal abdominal ring.” As this ring looks towards the interior of the abdomen, and forms the entrance of the funnel-shaped canal, it cannot of course be seen from before until we slit open this canal. Compare the parts marked H h in Plates 30 and 31.
The inguinal and iliac portions of the fascia transversalis join along the line of Poupart’s ligament, A C. The iliac vessels, in their passage to the thigh, encounter the fascia at the middle third of the crural arch formed by the ligament, and take an investment (the sheath, R) from the fascia. The fore part of this sheath is mentioned as formed by the fascia transversalis—the back part by the fascia iliaca; but these distinctions are merely nominal, and it is therefore unnecessary to dwell upon them. The sheath of the femoral vessels is also funnel-shaped, and surrounds them on all sides. Its broad entrance lies beneath the middle of Poupart’s ligament. Several septa are met with in its interior. These serve to separate the femoral vessels from each other. The femoral vein, O, Plate 30, is separated from the falciform margin, S s, of the saphenous opening by one of these septa. Between this septum and the falx an interval occurs, and through it the crural hernia usually descends. These parts will be more particularly noticed when considering the anatomy of crural hernia.
Beneath the fascia transversalis is found the subserous cellular membrane, which serves as a connecting medium between the fascia and the peritonaeum. This cellular membrane may be considered as the seventh inguinal layer. It is described by Scarpa (sull’ Ernie) as forming an investment for the spermatic vessels inside the sheath, where it is copious, especially in old inguinal hernia. It is also sometimes mixed with fatty tissue. In it is found embedded the infantile cord—the remains of the upper part of the peritoneal tunica vaginalis—a structure which will be considered in connexion with congenital herniae.
By removing the subserous cellular tissue, we lay bare the peritonaeum, which forms the eighth layer of the inguinal region. Upon it the epigastric and spermatic vessels are seen to rest. These vessels course between the fascia transversalis and the peritonaeum. The internal ring which is formed in the fascia, K h, may be now seen to be closed by the peritonaeum, I. The inguinal canal, therefore, does not, in the normal state of these parts, communicate with the general serous cavity; and here it must be evident that before the bowel, which is situated immediately behind the peritonaeum, I, can be received into the canal, H h, it must either rupture that membrane, or elongate it in the form of a sac.
The exact position which the epigastric, L, Plate 31, and spermatic vessels, M, bear in respect to the internal ring, is a point of chief importance in the surgical anatomy of the groin; for the various forms of herniae which protrude through this part have an intimate relation to these vessels. The epigastric artery, in general, arises from the external iliac, close above the middle of Poupart’s ligament, and ascends the inguinal wall in an oblique course towards the navel. It applies itself to the inner border of the internal ring, and here it is crossed on its outer side by the spermatic vessels, as these are about to enter the inguinal canal.